diff --git a/docs/index.rst b/docs/index.rst
index eed05518..60357e2d 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -1,5 +1,13 @@
 .. include:: README.rst
 
+.. note::
+
+   Because the Datastore client uses the :mod:`grpcio` library by default
+   and uses third-party :mod:`requests` library if the GRPC is disabled,
+   clients are safe to share instances across threads.  In multiprocessing
+   scenarios, the best practice is to create client instances *after*
+   :class:`multiprocessing.Pool` or :class:`multiprocessing.Process` invokes
+   :func:`os.fork`.
 
 API Reference
 -------------